Power tools such as nut runners, drills, grinders, sanders, or similar type tools provide a rotating shaft at a given speed and torque. Depending on the function being performed, it is often advantageous to provide a rotating shaft at different speeds and different torques. The speed and torque of a rotating shaft may be altered through the use of gears.
When using a power tool to rotate a fastener, it is often desirable to rotate the fastener at a high speed throughout the fastening process until the fastener is almost tightened or otherwise meeting with additional resistance. During final tightening or increased resistance, it is often advantageous to apply a low speed rotation with a higher torque. The speed and torque of a rotating shaft in a power tool may be altered by engaging and disengaging various gears. The engaging and disengaging of gears for changing the speed and torque of the rotating shaft may be accomplished through clutch members operable in response to fluid pressure.
Disadvantages of known speed shifting mechanisms may include component deterioration, jammed parts and frequent maintenance. Some types of speed shifting devices used in power tools do not provide for an adjustable torque setting. Other disadvantages with gear shifting power tools may include using fluid driven clutch members for engaging and disengaging gears that tend to be expensive, less reliable, and maintenance intensive. Other disadvantages may include shifting a power tool from a relative high speed/low torque rotation to a relative low speed/high torque rotation without a mechanism or means to ensure that the power tool will maintain the low speed/high torque condition so that proper tightening may be applied or so that a proper or desired torque may be applied. Additionally, some devices require two motors in order to achieve the high torque needed for a final tightening; one motor may rotate the output for a high speed/low torque output while another motor is added to achieve the high torque needed for final tightening.